Electric measuring instrument.



B. THOMSON. ELECTRIC MEASURING INSTRUMENT. APPLIGATION TILED NOV. 13.1907.

927,1 91 Patented July 6, 1909.

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Witnesses:

Inventor: Elihu Thomson,

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E. TH 0 MSON ELECTRIC MEASURING INSTRUMENT.

APPLICATION FILED NOV. 13, 1907.

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Inventor Elihu Thomson,

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' Witnesseg/ v 41 UNITED STATES PATENT OFFICE.

ELIHU THOMSON, OF SWAMPSCOTT, MASSACHUSETTS, ASSIGNOR TO GENERALELECTRIC COMPANY, A CORPORATION OF NEW YORK.

ELECTRIC MEASURING INSTRUMENT.

To all whom it may concern:

Be it known that I, ELIHU THOMSON, a citizen of the United States,residing at Swampscott, county of Essex, State of Massachusetts, haveinvented certain new and useful Improvements in Electric MeasuringInstruments, of which the following is a specification.

My invention relates to electric measuring instruments and moreparticularly to indi cating instruments comprising a permanent magnetwith a movin current carrying coil mounted to move in t 1e field of themagnet and having a pointer movable over a scale to show the extent ofmovement of the coil.

It is desirable that an indicating instru ment have a long open scalewith practically uniform subdivisions so that the instrument may beeasily read, and it is also often desirable that the instrument be moresensitive at predetermined parts of the scale than at the other parts,or 1n other words, that the scale be unusually open. In the usual typesof instrument the scale is about 90 in extent, which causes the scaledivisions to be so small that it is diificult to read the instrument,and the scale cannot be made open at any desired point.

The object of my invention is to provide an. instrument having a longscale with uniform divisions and which may, if desired, be madeabnormally sensitive to any arbitrarily selected point or points of thescale so that the scale may be opened out whenever desired.

In carrying out my invention the current carrying coil which ispreferably flat and mounted to move edgewise through the fieldmaintained. by the permanent magnet, is so shaped that equal movementsin any part of its path cause equal changes in the number of lines offorce included by it, thereby producing a scale which is uniform fromend to end. If the field produced by the magnet is uniform a rectangularcoil with straight sides mounted to move edgewise in the field gives ascale which is ractically uniform, but is comparatively s ort, sincewhere the coils move about a pivot as a center so that the scale iscircular, two rectangular coils must be mounted upon the periphery of asupport rotatable about the ivot and as each coil occupies about halfthe periphery, the scale becomes less than. a semicircle in extent. Thescale may be made to extend through nearly a complete circle byarranging the Specification of Letters Patent.

Application filed. November 13, 1907.

Patented July 6, 1909.

Serial NO. 401,948.

field and the coil in such relation to each other, referably by properlyshaping either the fiel d or the coil, that the coil progressivelyincludes more and more lines of force as it turns through nearly acomplete circle, while in the usual type of instrument the coil hasincluded the maximum number of lines by the time it has turned throughabout 90. The desired result may be attained by making the coiltriangular and mounting it to move along a line from the apex to thebase of the triangle into a magnetic field which extends through only afraction of the arc of movement of the coil. The magnet preferably hasconcentric pole pieces and the coils are shaped so as to move bodilyedgewise into or out of the intense and uniform field existing in theannular gap between the pole pieces.

The scale of the instrument may be opened at any selected point orpoints by changing the shape of the moving coil so that the number oflines of force included by the coil changes arbitrarily as the coilmoves and bears no fixed or definite relation to the extent so that thescale may be opened out at one or several different points.

One of the various forms in which my invention may be embodied is shownin the accompanying drawings, in which- Figure 1 is a plan view of ameasuring instrument; Fig. 2 a perspective view of the moving coil andsupport of the instrument shown in Fig. 1; Fig. 3 a sectional view ofthe instrument shown in Fig. 1; Fig. 4 is a developed view of one formof current carry ing coil; Fig; 5 a developed view of another form ofcurrent carrying coil; Fig. 6 a view of the magnetic system of theinstrument; an d. Fig. 7 is a plan view of the pole piece and. coil ofthe form of instrument having a very long scale.

The instrument shown in the drawings comprises a base for carrying themoving parts and a cover of any suitable form secured to the base. Thecurrent is led to the instrument through terminals of any suitable formmounted on the base and through a com ensating resistance such as iscommon y used in connection with measuring instruments of this type.

The permanent magnet 1 of the instrument is referably arranged toproduce a uniform 'eld of force and in the instrument illustrated isbent to the form shown in Fig.

6. The magnet has a semicircular pole piece Qextending through about 180and a cylindrical pole piece 3 concentric with the circular pole pieceand separated from it by an annular air gap in which exists an intenseand uniform magnetic field of an extent dependent on the length. of thepole piece 2. The moving parts of the instrument are supported in properrelation to the magnet by means of pedestals 4 secured to the magnet andcarrying a cross-piece 5 which is provided. with a bearing 6 for theupper end. of an arbor or pivot 7 which is mounted concentric with theaxis of the pole piece 3 and has its lower endinounted in a suitablehearing on the upper end of said pole piece. The arbor or pivot 7carries a cylindrical support or spool 8 mounted concentric with thepole piece 3 to move in the annular air-gap between the pole pieces. Thesupport or pool 8 is made of aluminum or similar material and acts as asupport for the current carrying coil and also to damp the movement ofthe coil and render the instrument deadbeat. The extent of the movementof the support or spool 8 is regulated by a restraining s n'ing 9 of anywell known form with one end attached to the arbor 7 and the other endto a stationary member secured to the cross-piece 5. The extent of themovement of the support 8 is indicated by means of a pointer 10 movableover a scale plate 11.

The current carrying coil of the instrument is mounted. upon and securedto the support or spool 8 and is preferably wound flat and mounted uponthe support so as to have a bodily edgewise movement through the uniformfield in the gap between the poles. The preferred form of coil for auniform scale of measurement is rectangular, two coils being mounted onthe support 8 in the manner shown in Fig. 5 so as to move edgewisebetween the poles of the magnet 1 and cooperates in turning the support8. With this arrangement, however, the scale is somewhat less than 180though uniform from end to end. -When the instrument is required to havea long scale, a triangular coil 13 of the form shown in Fig. 4 ismounted upon the cylindrical support or spool to move through a verynarrow field secured by the use of a very narrow pole piece 2 as shownin Fig. 7, instead. of the semi-circular pole piece 2 and a scale ofnearly 360 degrees may be secured since the triangular coil can bearranged to practically encircle the support, and in moving into and outof the nar row field will rotate the support nearly a completerevolution. When the pole piece is made wider, as shown in Figs. 2, 3and 6, and produces practically a semi-circular field, the triangularcoil will have a movement of about 180. The coil is mounted as shown inFig. 2 so as to be movable along a line from the apex to the base of thecoil with the straight sides of the coil forming an angle with the planeof movement of the coil. Vith this construction the coil cuts the linesof force at a uniform rate and may be arranged with the apex justentering the field at zero position so as to be drawn into the field offorce by the small end or else to be completely immersed in the field offorce at the ZOl'O position and to be forced out of the field whencurrent flows through the coil.

With the forms of coil above described the number of lines of forceincluded in any position varies directly as the extent of movement ofthe coil and the scale is uniform, but the shape of the moving coil maybe varied in any arbitrary way to open out the scale as desired. Thecoils may be given any desired form to secure this result but preferablythe triangular coil is made with wavy or crooked sides.

My invention may be embodied in many other forms than that shown anddescribed and I, therefore, do not wish to be restricted to the preciseform disclosed but intend to cover by the appended claims all changesand modifications within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is,

1. An electric measuring instrument comprising means for producing amagnetic field, a rotatable support, and. a current carrying coilmounted on said support, said field and said coil being shapedrelatively to each other to cause the number of lines of force includedby the coil to vary progressively during a substantially completerotation of said support.

2. An electric measuring instrument comprising means for producing amagnetic field, a rotatable support and a fiat current carrying coilmounted on said support in such relation to the field that the number oflines of force included by the coil varies progressively during acomplete rotation of the sup port.

3. An electric measuring instrument comprising means for producing amagnetic field and a current carrying coil rotatably mounted. in saidfield, said coil and field being of dissimilar shape and so related thatthe coil includes a progressively increasing flux within the coilthroughout substantially a complete rotation of the support.

4. In a measuring instrument, the combination with means for producing amagnetic field of uniform density, of a triangular current carrying coilmounted for bodily edgewise movement in said field along a line from theapex to the base of the triangle.

5. In a measuring instrument, the combination with means for producing amagnetic field, of a triangular coil mounted for bodily translationedgewise through said field along a line from the apex to the base ofsaid coil and longer in the direction of its movement than the extent ofsaid field in said direction, and an indicator connected to said coil.

6. In a measuring instrument, the combination with means for producin auniform magnetic field extending throug a definite angular distanceabout a center, of a current carrying coil extending through a greaterangular distance than said field mounted for bodily movement edgewiseabout said center and tapering to include more lines of force as therange of deflection increases.

7. In a measuring instrument, the combination with means or producing amagnetic field of definite width, of a triangular current carrying coilmounted to move edgewise in the magnetic field along a line from theapex to the base of the coil and having a length in the direction ofmovement greater than the width of the field.

8. In a measuring instrument, the combi nation with means for roducing auniform magnetic field, of a coil formed as an isosceles triangle andmounted for bodily edgewise movement at right angles to the base.

9. In an indicating instrument, the combination with a magnet havinconcentric pole pieces, of a fiat coil bent to Form a portion of ahollow cylinder concentric with said pole pieces and mounted to moveedgewise between. said pole pieces, and a controlling tween said polepieces, a control spring connected to said coil to normally hold it withone edge within said field and the remainder of the coil outside saidfield, whereby said coil includes more lines of force as it movesagainst said spring.

11. In a measuring instrument, the combination with a magnet havingconcentric pole pieces, of a cylindrical support pivoted concentricallywith said ole pieces, and a triangular coil shaped to t and attached tothe surface of said support to move between said pole pieces.

In witness whereof, I have hereunto set my hand this eleventh da ofNov., 1907.

ELIII THOMSON.

WVitnesses:

JOHN A. McMANUs, J1:., A. F. MACDONALD.

